Till now you could use a b/w image as a keying mask for creating transition effects.But what would be very nice is to get an option to set the treshold for the key. I mean that everything over a definable value (0-255) in the mask would be keyed out in the source. With a seconed value you could set the range for the key to get a smooth/transparent transition. And at last this values should be variable by the use of keyframes.

So in the end I could creat an animated lumakey by running trough the luma values from 0 to 255 with a specific feathering.